When importing several CPTs, this was accumulating row fields values.
Updated like this:
$the_values = null;
foreach ($years as $index => $years) {
$the_values[] = array(
$subfield_key_1 => $years,
$subfield_key_2 => $tax_01[$index],
$subfield_key_3 => $tax_02[$index],
$subfield_key_4 => $tax_03[$index],
);
update_field($field_key, $the_values, $post_id);
}